There are several Scheme implementations that are well suited to building "something big". Someone mentioned Racket, but there's also e.g. Chicken Scheme or Gau

There are several Scheme implementations that are well suited to building "something big". Someone mentioned Racket, but there's also e.g. Chicken Scheme or Gauche, both of which come with a sizable collection of libraries to do real-world stuff. Then there are implementations like Scheme48, which seem to be tailored to building something "on top" of it.